1. Field of the Invention
This invention relates generally to the manufacture of laminated transparencies, e.g. laminated automotive transparencies, and, more particularly, to shaped, laminated automotive sidelites and to methods of making the sidelites.
2. Description of the Currently Available Technology
Typically, automotive windshields include two xe2x85x9xe2x80x3 (3.2 mm), shaped annealed glass plies secured together by a 0.030xe2x80x3 (0.76 mm) polyvinyl butyral interlayer. Examples of automotive windshields and methods of making the same are disclosed in U.S. Pat. Nos. 4,820,902; 5,028,759; and 5,653,903, which are herein incorporated by reference.
As can be appreciated by those skilled in the art, the processes of making laminated windshields are not easily adapted to making other types of laminated automotive transparencies, such as sidelites. For example, the glass blanks used in the manufacture of laminated windshields are typically annealed glass. On the other hand, glass blanks used in the manufacture of sidelites are typically tempered glass. Tempered sidelites are preferred to prevent damage to the sidelites during normal operation, e.g. door slamming, rolling the sidelites up and down, etc. The processing parameters and methods of treating annealed glass may not necessarily be translated directly for use with tempered glass.
Further, windshields are generally made from two glass plies, each xe2x85x9xe2x80x3 (3.2 mm) thick. The commercial production and shaping of glass sheets for windshields usually includes positioning one flat sheet on top of another flat sheet, heating the two stacked flat glass sheets in a furnace to the softening point of the glass, simultaneously shaping the heated glass sheets to a desired curvature and then cooling the bent glass sheets in a controlled manner to anneal the sheets. Conventional sidelites, on the other hand, are usually made from a single flat glass sheet or blank having a thickness in the range of 4 to 5 mm. The flat glass sheet is heated, shaped and tempered. The heating, bending and shaping of thinner glass blanks is more difficult than for thicker glass blanks. Thinner glass blanks pose problems in shaping and tempering due to the lesser ability of thinner glass blanks to retain heat. More particularly, as the thickness of the glass blank decreases, the rate of heat loss increases, and the heat initially imparted to the glass blank is quickly dissipated upon leaving the heating atmosphere of the furnace.
Generally, in the process of making sidelites, flat glass is shaped to defined curvatures or contours dictated by the shape and outline of the frames defining the window openings and window channels into which the sidelite is to be installed. By convention, most commercial vehicles have window channels configured for use with sidelites having a total thickness of about 4-5 mm. Therefore, in order to be integrated into an existing window channel without requiring extensive reengineering and also to be able to be retrofitted into existing vehicles, a laminated sidelite should preferably be of about the same thickness.
EP 0 600 766 discloses a laminated panel having a body with at least three layers of silicate glass and at least two intermediate layers of thermoplastic, with a total thickness of 6.0-9.0 mm. The panel has a thinner, stepped edge which can be inserted into a fixed side window guide, but the panel cannot be rolled up or down as a conventional vehicle sidelite due to the thickness of the panel body.
U.S. Pat. No. 5,198,304 discloses a laminated sidelite having different amounts of tempering in viewing and marginal areas to avoid tempering process deformations. This requires cooling different portions of the heated glass at different rates.
Another drawback in making laminated sidelites not encountered when making windshields is the problem associated with heating glass sheets having a functional coating, such as a solar control coating. Making laminated sidelites, rear windows and/or sunroofs having such a coating only on one blank is more difficult than making coated laminated windshields. More particularly, in the manufacture of windshields one surface of a flat blank is coated and a second flat blank, usually uncoated, is positioned, i.e. superimposed, over the first coated blank. The overlying blanks are heated, shaped and annealed simultaneously. In the manufacture of laminated, coated sidelites, rear windows and/or sun roofs, a coated flat blank and an uncoated flat blank are separately heated, shaped and heat treated. Because one blank is coated and the other uncoated, the shapes of the heat-treated coated and uncoated blanks do not match and are not compatible for lamination.
As can be appreciated by those skilled in the art of making automotive sidelites, it would be advantageous to provide a laminated automotive transparency, e.g., a sidelite, and a method of making the same that reduce or eliminate the problems discussed above.
This invention relates to a laminated article, e.g., an automotive sidelite, including a first ply secured to a second ply by a sheet of interlayer material. The first ply has a concave surface with a predetermined concave shape and the second ply has a convex surface with a predetermined convex shape. The concave surface may have a smaller radius of curvature than the convex surface. The laminated sidelite has a total thickness of about 3.0 mm to about 6.0 mm, preferably of about 4.0 mm to about 5.0 mm. Each ply is a heat treated, e.g., tempered or heat strengthened (at least partially tempered) glass ply having a thickness of less than about 3.0 mm, preferably about 1.0 mm to about 3.0 mm, and more preferably about 1.6 mm to about 2.1 mm. The interlayer material is preferably a plastic material, such as polyvinyl butyral or the like, and has a thickness of less than about 0.80 mm, preferably between about 0.50 mm to about 0.80 mm. A functional coating, such as but not limited to a solar control coating, a low emissivity coating having at least one dielectric layer and at least one infrared reflective layer, an electroconductive coating, a heatable coating, or an antenna coating can be incorporated into the laminated article, e.g., by providing a coating on the first ply concave surface by depositing or forming the coating.
This invention further relates to a method for producing the laminated article of the invention, e.g., an automotive sidelite. The method includes providing first and second blanks and then preferably using different techniques and parameters to heat, shape and heat treat the blanks to form first and second plies having predetermined concave and convex surfaces, respectively. The first blank has a functional coating provided over at least a portion of a major surface thereof. The coated first blank is heated by supplying heat principally or primarily, if not totally, toward the uncoated side of the first blank. The heating temperature is controlled by sensing the temperature substantially adjacent the uncoated side of the first blank, e.g., adjacent a furnace conveyor supporting the first blank. The second, uncoated blank is heated by supplying heat toward both sides of the second blank. Heating the second blank is controlled by sensing the temperature on both sides of the second blank, e.g. by sensing and controlling the temperature of heaters located above and below the furnace conveyor and preferably sensing the temperature below the second blank and adjacent the conveyor supporting the second blank and controlling both the top and bottom heaters. The first and second blanks may be shaped, e.g. by different shaping surfaces, such that the concave surface has a smaller radius of curvature than the convex surface. However, the predetermined concave and convex surfaces are substantially similar for the laminated surfaces to substantially match when the first and second plies are laminated together about an interlayer.